Grinders, shredders, or comminution mills are well known devices for reducing the particle size of a material. For example, U.S. Pat. No. 5,192,029 to Harris (hereinafter Harris) and U.S. Pat. No. 5,680,994 to Eide et al. (hereinafter Eide) each disclose mills for grinding garbage. Each of theses mills includes a rotor rotatably mounted in a generally octagonal housing. The rotor includes a generally vertical shaft and a plurality of blades or hammers mounted on the shaft. Garbage is admitted into the housing through an inlet near the top of the housing and is impacted by the blades of the rotor. Material of a reduced particle size is removed from the mill through an outlet near the bottom of the housing. The ground garbage can be sent to a landfill where it will take up less room than unprocessed garbage, or it can be composted or recycled depending on the included materials. If the material is to be shipped, it can be shipped more efficiently due to its reduced size and greater density.
The mill of Eide also includes a fan or impeller that is mounted on the rotor shaft below the cutting blades. The fan is intended to create airflow that acts to move material through the mill and to expel it from the outlet. The airflow also aids to remove moisture from the material as it is being ground. The fan generally comprises a fan disc mounted to the rotor shaft. The fan disc includes a plurality of radially extending lengths of angle iron mounted thereon. One flange of each angle iron is fixedly bolted to the fan disc and the other extends upwardly from the disc to act as a fan blade.
Mills such as those described by Harris and Eide have several drawbacks. All or parts of the blades may sheer off during grinding operations. Pieces of the blades can be torn away from the blade via contact with the materials being ground or the blades themselves can be torn or ripped away from their coupling with the rotor. The loose blade portions can damage other blades and components inside the grinder and are likely discharged through the outlet as contaminates in the ground materials. Another drawback to these designs is the need for the fan or impeller to generate airflow through the mill. These add additional components and complexities to the manufacture and maintenance of the mill. It would be advantageous to provide a comminution mill with non-rigid impact blades or impact arms and that does not require a fan or impeller to generate airflow therethrough.